This invention relates to a method for preparing a norbornene structure compound that can be employed as an intermediate product for preparation of medical or agricultural chemicals or as a monomer for preparation of polymers.
The norbornene structure compound represented by the formula (2) ##STR3## wherein l, m and n are integers of 0.ltoreq.l.ltoreq.3, 0.ltoreq.m.ltoreq.8 and 1.ltoreq.n.ltoreq.3, respectively, and each of R.sup.1 to R.sup.6 is a hydrogen atom or a hydrocarbon residue having 1 to 3 carbon atoms and R.sup.6 may form a ring with R.sup.4 or R.sup.5, has an active double bond of norbornene ring and can be converted into useful medicines or agricultural chemicals upon addition of a variety of organic or inorganic compounds to this double bond. Also the compound represented by the formula (2) may be employed alone or in combination with other olefins as a monomer for cationic or coordinated anionic polymerization or for ring-opening polymerization employing metathesis catalysts. Recently, there is an increasing demand for polymers that are prepared from the above mentioned monomers and that may be useful for optical applications, such as optical disks, or for polymers prepared upon thermal or cationic polymerization which polymers exhibit superior weather- and heat-resistance, transparency and color on account of not having unsaturated bonds. However, the compounds (2) that can be used for these usage cannot be prepared without considerable difficulties. There is so far known a method for preparing the compound of the formula (2) by the Diels-Alder reaction of cyclopentadiene or a compound capable of producing cyclopentadiene in the reaction system, such as dicyclopentadiene, with monoolefins, such as butene-1, pentene-1, pentene-2, cyclopentene, hexene-1, hexene-2, hexene-3, 3-methyl-1-butene, 2-methyl-2-pentene, 3-methylcyclohexene, 2-methyl-2-hexene, 3-methyl-2-hexene, ethylnorbornene, n-propylnorbornene, isopropylnorbornene, ethyl-1,4,5,8-dimethano-1,2,3,4,4a,5,8,8a-octahydronaphthalene, n-propyl-1,4,5,8-dimethano-1,2,3,4,4a,5,8,8a-octahydronaphthalene, isopropyl-1,4,5,8-dimethano-1,2,3,4,4a,5,8,8a-octahydronaphthalene, 2,3,3a,4,7,7a-hexahydro-4,7-methano-1H-indene, 2,3,3a,4,4a,5,8,8a, 9,10-decahydro-4,9,5,8-dimethano-1H-benzindene, as exemplified in the following equations (3) to (6). ##STR4##
The practical example of synthesis for ethylnorbornene and pentylnorbornene has been reported by Plate (Dokl. Akad. Nauk. SSSR, 105,989,991 (1955)) and that for endo- and exo-2,3,3a,4,7,7a-hexahydro-4,7-methano-1H-indene has been reported by Bruson et al. in Journal of American Chemical Society, vol. 67, pp723(1945) and vol. 70, pp2809(1948) et al.
However, in the Diels-Alder reaction between cyclopentadiene and monoolefin, the reaction rate is extremely low because no electron-withdrawing substituents are bonded to monoolefin, then the reaction has to be carried out at elevated temperature for a long time to raise the yield. To make matters worse, since the reaction is carried out under these hostile conditions, trimers, tetramers, pentamers or higher polymers of cyclopentadiene, or addition product of cyclopentadiene to the object compound represented by the formula (2), are by-produced in larger quantities, thus adversely affecting the selectivity of the object compound.
On the other hand, in the Diels-Alder reaction of cyclopentadiene and conjugated or non-conjugated polyene, double bonds not involved in the reaction with these polyenes act as electron-withdrawing groups, in a manner different from the aforementioned reaction of monoolefin as the reactant, such that the reaction rate is increased and the compound having the formula (1) ##STR5## wherein l, m and n are the same as those for the formula (2), can be produced easily. For example, dimerization of cyclopentadiene according to the formula (7) ##STR6## proceeds rapidly at an ambient temperature, while 5-vinyl bicyclo [2. 2. 1] hept-2-ene and tricyclopentadiene according to the formulae (8) and (9) ##STR7## may be produced easily at 60.degree. to 150.degree. C. The same may be said of the reaction shown by the formula (10) ##STR8##
It may be contemplated that the object compound represented by the formula (2) may be prepared by hydrogenation of the compound of the formula (1) that can be produced easily as described above. However, it was not possible with the conventional methods to produce the compound of the formula (2) with high selectivity. According to East German Patent No. 106,343 or report of I. S. Kolominkov (Izv. Akad. Nauk. SSSR, Ser. Khim, 1972 (5)1180), 5-vinyl bicyclo [2. 2. 1] heptane (A) is selectively produced by hydrogenation of 5-vinyl bicyclo [2. 2. 1] hept-2-ene as shown by the formula (11) ##STR9## but the object compound of 5-ethyl bicyclo [2. 2. 1] hept-2-ene (B) is not produced. According to Japanese Patent Publications Nos. 34811/1973 and 45391/1976, Japanese Laid-open Patent Publications Nos.4158/1976 and 95648/1977 and reports by C. A. Brown (J. Chem. Soc.,D,1969(17),952), upon hydrogenation of dicyclopentadiene or tricyclopentadiene, a mixture of 2,3,3a,4,7,7a-hexahydro-4,7-methano-1H-indene (C) and 3a,4,5,6,7,7a-hexahydro-4,7-methano-1H-indene (D), as shown by the formula (12) ##STR10## is obtained, but the compound D accounts for the major portion of the product and the object compound (C) is produced only in minor quantities.
It is reported by Yu. G. Osokin et al in Dokl. Akad. Nauk. SSSR, 220 (4), 851(1975), Ser. Khim that, upon hydrogenation of 5-vinyl bicyclo [2. 2. 1 ] hept-2-ene, 5-ethyl bicyclo [2. 2. 1 ] hept-2-ene is produced in a slightly larger amount than 5-vinylbicyclo [2. 2. 1] heptane. It is also reported by W. Keim et al. in Chem.-Ing.- Tech., vol. 55, pp906(1983) that, with hydrogenation of dicyclopentadiene, the yield ratio of (C)/(D) in the formula (12) of the order of 5/4 may be obtained, while it is reported by K. M. Nicholas in Journal of American Chemical Society, vol. 97, pp3254 (1975) that the object compound (C) may be obtained by a method of protecting the highly reactive double bond at the 5 and 6 positions of dicyclopentadiene with an iron carbonyl compound. It is apparent that the methods shown in these reports provide improved selectivity in comparison with the preceding examples in consideration of the difference in reactivities between the two double bonds. However, it is still not possible with these methods to produce the compound of the formula (2) with high selectivity or to produce the compound on an industrial scale.
On the other hand, Ziegler type catalysts are known to exhibit hydrogenation acitivity, as reported in detail in "Homogeneous Hydrogenation", page 363, by B. R. James, J. Wiley & Sons, New York, 1973.
However, it has not so far been known that the compound represented by the formula (1) may be hydrogenated to the compound represented by the formula (2) with high selectivity in the presence of the Ziegler type catalyst.